Tenofovir alafenamide (TAF) is a nucleotide reverse transcriptase inhibitor useful for the treatment and prevention of HIV and HBV. TAF hemifumarate is described in U.S. Pat. No. 8,754,065 (incorporated by reference herein in its entirety). U.S. Pat. No. 6,043,230 (incorporated by reference herein in its entirety) and other publications describe the antiviral specificity of nucleotide analogs, such as tenofovir disoproxil.